Abstract

The phosphorylation of mu opioid receptors (MOPr) by G protein-coupled receptor kinase(s) (GRKs) followed by arrestin binding is thought to be a key pathway leading to desensitization and internalization. The present study used the combination of intracellular and whole cell recordings from rats and mice along with live cell imaging of epitope-tagged FlagMOPr from mouse locus coeruleus (LC) neurons to examine the role of protein kinases in acute desensitization and receptor trafficking. Inhibition of GRKs using heparin or a GRK2 mutant mouse did not block desensitization or alter the rate of recovery from desensitization. The non-selective kinase inhibitor, staurosporine did not reduce the extent of [Met5]enkephalin (ME)-induced desensitization but increased the rate of recovery from desensitization. In the presence of staurosporine, ME-activated FlagMOPr was internalized but did not traffic away from the plasma membrane. The increased rate of recovery from desensitization correlated with the enhancement in the recycling of receptors to the plasma membrane. Thus ME-induced MOPr desensitization persisted and the trafficking of receptors was modified after inhibition of protein kinase(s). The results suggest that desensitization of MOPr may be an early step following agonist binding that is modulated by, but not dependent on kinase activity.